The present invention relates to an electric overhead trolley system for conveying and positioning loads, having at least one motor-driven travelling gear adapted for being displaced along a track, a driving wheel supported on the track and at least one auxiliary wheel which influences the frictional engagement between the driving wheel and the track and which interacts with an auxiliary track extending in parallel to the track, at least along certain sections.
Electric overhead trolley systems--also known as single-track overhead conveyers--have been in use in production operations for transporting objects, which are to be processed or on which additional parts have to be mounted, between different locations within the production plant.
Each conveying unit may in this case consist of one, two or more travelling gears which may be interconnected by transverse girders on which the objects to be conveyed are hooked up and unhooked, respectively
Compared with drag-chain conveyers, for example, such conveyers provide the advantage that each conveyer unit can be operated independently of the others. On the other hand, however, it is a disadvantage that such conveyers cannot overcome all gradients. Generally, the gradients which can be overcome, i.e. the so-called vertical lift, are limited to the range of 6 to 8 degrees.
This circumstance, namely that greater gradients cannot be overcome, is due to the fact that the conveyer is moved by frictional force so that in the event of greater gradients this frictional force will no longer suffice to overcome such gradient. In an effort to overcome this drawback, it has been proposed to arrange an auxiliary wheel below the conveyer track, which is preferably designed as an I beam, which auxiliary wheel then exerts an additional force on the driving wheel so as to increase the frictional force. As an alternative, DE-PS 474 243 suggests to arrange an auxiliary track above the conveyer track, which auxiliary track supports an auxiliary wheel mounted at one end of a double lever. The double lever can be pivoted about the axis of the driving wheels. Its other end carries an auxiliary counter-gear which acts to urge the driving wheels against the track.
In the case of these solutions, however, the driving force is still transmitted to the track only by the driving wheel. The auxiliary wheel does not in any way contribute to the transmission of the driving force. Instead, it only acts to increase the contact pressure of the driving wheel.